Ultrasonic touch and force input detection

ABSTRACT

Touch events can be detected using an ultrasound input device coupled to a surface, such as a surface of a piece of furniture or electronic device. The ultrasound input device can generate ultrasonic waves in the surface, the reflections of which can be measured by the ultrasound input device. When a touch is made to the surface (e.g., opposite the ultrasound input device), the physical contact can absorb some of the energy of the outgoing ultrasonic waves (e.g., the originally transmitted wave and any subsequent outgoing reflections). Energy measurements associated with the measured reflections can thus be used to identify touch events. Various techniques can be used to make the energy measurements and reduce identification of false touch events.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Patent ApplicationNo. 62/674,317 filed May 21, 2018 and entitled “ULTRASONIC TOUCH ANDFORCE INPUT DETECTION” and U.S. Patent Application No. 62/725,697 filedAug. 31, 2018 and entitled “ULTRASONIC TOUCH AND FORCE INPUT DETECTION,”which are both hereby incorporated by reference in their entirety.

BACKGROUND

Capacitive, resistive and inductive sensing are used in industrial,automotive, medical, and consumer applications to detect touch inputs.The use of capacitive technology to detect a touch input has grownrapidly in human interface devices (HID), such as track-pads andtouch-screens. Consumer and industrial applications are beginning toadopt touch-buttons and sliders using capacitive technology in devicessuch as mobile phones, TV controls, automotive dashboards, remotecontrols, or industrial controls. Capacitive sensing has proven to bemuch more appealing than mechanical switches and rotary encoders, bothin terms of looks and reliability.

However, the use of capacitive, resistive, or inductive sensing limitscreative industrial designs due to challenges in touch input layout andsystem stack up. Conflicting priorities between design and robustnessfurther complicates the design. It is also to be noted that presentinput touch sensing methodologies cannot be implemented on metalsurfaces. In addition, current sensing technologies has inherentproperties that limit water-proof applications. Pressure sensingtechnologies using strain gauges have emerged as alternative sensingtechnologies for metal surface touch input. However, the measurement ofdeflection and strain is often unreliable, specifically in metals.Additional sensing layers (e.g., capacitive) are required to detect anx-y position of an input touch detected using a strain gauge. Increasedcomplexity in touch input interface materials, the implications ofcomplex interfaces on industrial designs, water-proofing, and cost havebeen key challenges limiting the use of touch-inputs in any environmentand in with any material. There is a need for improved systems andmethods of detecting touch inputs to human machine interfaces (HMI).

Embodiments of the invention address these and other problems,individually and collectively.

BRIEF SUMMARY

A touch input solution is provided for improving detection of touchinputs in HMIs. An ultrasound input device can detect the presence of anobject on any surface with a sensor positioned on the reverse side ofthe surface material. The ultrasound input device enables creativedesigns without disruption of product skin or design material. Such anultrasound input device can be implemented in various devices, e.g.,input touch buttons, sliders, wheels, etc. The ultrasound input devicecan be deployed under surfaces comprising a variety of materialssimplifying industrial designs and appearance. Furthermore, a grid ofthe ultrasound input device buttons can be implemented to create keypad, mouse pad, or touch input on any surface anywhere. An ultrasoundinput device allows touch input deployment of an HMI on surfacescomprising wood, leather, glass, plastic, metal (e.g., aluminum orsteel), ceramic, plastic, a combination of one or more materials, etc.

A touch input device implemented using an ultrasound input device candetect a touch input associated with a specific material. For example,an ultrasound input device can distinguish between a touch input from aglove and a touch input from a finger (each having a differentreflection/transmission of the ultrasound when touching the material)and thus be configured for only glove triggering. This type of inputtouch control is ideal for medical devices. A touch input buttonimplemented using an ultrasound input device can be easily implementedon aluminum, glass, titanium, and ceramic surfaces, replacing mechanicalsmartphone buttons.

An ultrasound input device provides an improvement to the aestheticfeatures and reliability of touch input detection over capacitive andmechanical devices. A button can be implemented on a surface by definingthe button area on a touch surface. An ultrasound input device can beembedded/placed behind the surface and thus limits environmentalexposure including dust and moist. An ultrasound input device canincrease flexibility of button programmability options. For example, auser can define the functionality of the button through a systemcontroller. In some embodiments, the system controller can monitor userbehaviors to improve machine/system preferences and performance. Anultrasound input device mechanically coupled to a surface but positionedaway from view, such as underneath or behind an opaque surface, can beused to provide a hidden input not discernible or not easilydiscoverable to those who do not already know its location. Anultrasound input device can be low powered and battery powered, such asto operate for extended periods of time without requiring directconnection to a mains power source. An ultrasound input device can be orbe incorporated into an internet of things (IOT) device capable ofproviding sensor data (e.g., a button press) to other devices on a localor remote network.

Multiple touch input detection (e.g., number of taps on the buttons orhold or swipe to different directions) can be used to increase thefunctionality of a single input device. In some embodiments, anultrasound input device can also enable detection of specific objects asa source of a touch input. For example, an ultrasound input device canbe configured to activate the button based on material characteristicsof the object. Furthermore, an ultrasound input device allows formonitoring of the touch input. For example, a vehicle using one or moreultrasound input devices can monitor a hands-on steering wheelrequirement when auto-pilot is disengaged.

The analog and digital circuits necessary to operate the ultrasonictouch input can be integrated with the ultrasound transducers. Thisintegration allows for achieving very small chip height (e.g., less than0.5 mm) and foot print (e.g., less than 1 mm²) and enables input touchdetection in tight spaces. In some embodiments, the output from the chipcan be based on Inter-Integrated Circuit (I²C). This on-chip processingcan eliminate the need for separate analog chips for ultrasonic sensorsignal amplification and analog to digital conversion. The ultrasonictouch input sensor can process and output a signal indicating a touchinput independent from a main microcontroller or any other boardcomponent in the system in which the sensor is installed.

These and other embodiments of the invention are described in detailbelow. For example, other embodiments are directed to systems, devices,and computer readable media associated with methods described herein.

A better understanding of the nature and advantages of embodiments ofthe present invention may be gained with reference to the followingdetailed description and the accompanying drawings.

BRIEF DESCRIPTION

FIG. 1 is a schematic diagram depicting the effect of touch force on thereflected ultrasound signals in an ultrasound input system according tocertain aspects of the present disclosure.

FIG. 2 is a schematic diagram depicting an ultrasound input system in annon-contacted state and a contacted state according to certain aspectsof the present disclosure.

FIG. 3 is a schematic diagram depicting an ultrasound input deviceaccording to certain aspects of the present disclosure.

FIG. 4 is a cross-sectional view of two piezoelectric micromachinedultrasonic transducers bonded to a CMOS wafer according to certainaspects of the present disclosure.

FIG. 5 is a schematic diagram of a flow for digitally processingultrasound signals emitted and received by an ultrasound input deviceaccording to certain aspects of the present disclosure.

FIG. 6 is a schematic diagram of a flow for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration according to certain aspects of the present disclosure.

FIG. 7 is a schematic diagram of an example of a flow for processingultrasound signals emitted and received by an ultrasound input deviceusing energy integration according to certain aspects of the presentdisclosure.

FIG. 8 is a schematic diagram of a flow for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration via absolute value accumulation according to certain aspectsof the present disclosure.

FIG. 9 is a schematic diagram of a flow for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration via self-mixing and integration according to certain aspectsof the present disclosure.

FIG. 10 is a schematic circuit diagram depicting an analog integratorwith a negative bias current circuit according to certain aspects of thepresent disclosure.

FIG. 11 is a schematic diagram of a flow for processing ultrasoundsignals depicting the reduced effects of reflected ultrasonic signaltime-of-flight changes on touch input detection within an energymeasurement window according to certain aspects of the presentdisclosure.

FIG. 12 is a schematic diagram of an abbreviated flow for processingultrasound signals depicting the heightened effects of reflectedultrasonic signal time-of-flight changes on touch input detectionoutside of an energy measurement window.

FIG. 13 is a schematic diagram of a flow for processing ultrasoundsignals depicting the minimal effects of reflected ultrasonic signaltime-of-flight changes on touch input detection outside of an energymeasurement window when window shaping is used according to certainaspects of the present disclosure.

FIG. 14 is a schematic circuit diagram depicting a window shapingcircuit according to certain aspects of the present disclosure.

FIG. 15 is a schematic diagram depicting a flow for processingultrasound signals to detect a touch input using the amplitude ofreflected ultrasonic signals according to certain aspects of the presentdisclosure.

FIG. 16 is a chart depicting reflected ultrasonic signal measurementsmade using an ultrasound input device and illustrating techniques toimprove touch input detection according to certain aspects of thepresent disclosure.

FIG. 17 is a chart depicting reflected ultrasonic signal measurementsmade using an ultrasound input device and illustrating additionaltechniques to improve touch input detection according to certain aspectsof the present disclosure.

FIG. 18 is a set of charts depicting temperature dependence of reflectedultrasonic signals according to certain aspects of the presentdisclosure.

FIG. 19 is a set of charts depicting time-of-flight temperaturedependence of a two frequency method of detecting a touch inputaccording to certain aspects of the present disclosure.

FIG. 20 is a chart depicting reflected ultrasonic signal measurementsmade across several frequencies using an ultrasound input device andillustrating techniques to improve touch input detection according tocertain aspects of the present disclosure.

FIG. 21 is a schematic plan view depicting a two-frequency PMUT with aconcentric-circular design according to certain aspects of the presentdisclosure.

FIG. 22 is a schematic plan view depicting a multi-frequency ultrasoundinput device with a square design according to certain aspects of thepresent disclosure.

FIG. 23 is a chart depicting a machine learning decision algorithm usedto improve touch detection according to certain aspects of the presentdisclosure.

FIG. 24 is a schematic diagram depicting an electronic device with anultrasound input device according to certain aspects of the presentdisclosure.

FIG. 25 is a schematic diagram depicting an automotive component with anultrasound input device according to certain aspects of the presentdisclosure.

FIG. 26 is a schematic diagram depicting a keypad using an ultrasoundinput device according to certain aspects of the present disclosure.

FIG. 27 is a schematic diagram depicting a robotic arm using anultrasound input device according to certain aspects of the presentdisclosure.

FIG. 28 is a schematic diagram depicting a piece of furniture using anultrasound input device according to certain aspects of the presentdisclosure.

FIG. 29 is a schematic diagram of a piezoelectric resonator arraycontaining piezoelectric cantilevers usable in an ultrasound inputdevice according to certain aspects of the present disclosure.

FIG. 30 is a schematic diagram of a piezoelectric resonator arraycontaining piezoelectric pillars usable in an ultrasound input deviceaccording to certain aspects of the present disclosure.

DETAILED DESCRIPTION I. Device Overview

Embodiments of the invention are directed to an ultrasound input deviceto detect touch inputs. Specifically, embodiments are directed to anultrasound input device comprising a transducer coupled to a materiallayer that provides a surface to receive touch input signals to asystem. The ultrasound input device can be implemented using a varietyof material layers including wood, leather, glass, plastic, metal (e.g.,aluminum, steel, or others), stone, concrete, paper, polymers,biological materials (e.g., tissues, such as skin), a combination of oneor more materials, etc. The flexibility of material selection enablesthe use of an ultrasound input device in a variety of applicationsincluding front and side buttons of a mobile device; a steering wheel,infotainment unit, center console controls, mirrors, seats, doorhandles, windows, etc. of a vehicle; internet-of-things devices; medicaldevices such as bed controls, blood pressure measurement devices; inputdetection for robotics such as touch sensing for robotic fingers; andhidden input devices such as hidden within furniture or behind walls.

A. Detecting a Touch Input Using Ultrasonic Signals

FIG. 1 is a schematic diagram depicting the effect of touch on thereflected ultrasound signals in an ultrasound input device according tocertain aspects of the present disclosure. The ultrasound input device100 (also referred to as a touch sensor) can include a transducer 104coupled to a material layer 102. The material layer 102 has a first(interior) surface 106 and a second (exterior) surface 108. The materiallayer can be characterized by a distance 110 between the first surface106 and the second surface 108. The material layer 102 can be a covermaterial of a larger device that integrates an ultrasound input device.In some embodiments, the material layer 102 can form a body or a portionof the body of a device. In these embodiments, the first surface 106 canform an interior surface of the body and the second surface 108 can formthe exterior surface of the body. Second surface 108 can be consideredexterior as it is exposed to the environment. First surface 106 can beconsidered interior in that it is not the surface that contact is to bedetected or in that it is the surface where the transducer 104 isacoustically coupled to the material layer 102. FIG. 1 shows theultrasound input device with no touch 120, the ultrasound input devicewith a light touch 122, and the ultrasound input device with a heavytouch 124.

This touch sensor is triggered based on material acoustic properties oftouch surface (material layer 102) and the input object 112. Detectionof the light touch 122 is dependent on extent of reflected ultrasonicsignals 114 in the material layer 102 versus absorbed ultrasonic signals116 transmitted through the second surface 108 of the material layer 102into the input object 112. As used herein, a reflected ultrasonic signal(e.g., reflected ultrasonic signals 114) can refer to a signal that hasreflected off the second surface 108 of the material layer 102, and anabsorbed ultrasonic signal (e.g., absorbed ultrasonic signals 116) canrefer to a signal of which at least a portion of the signal has beenabsorbed by an input object 112 (e.g., a finger) contacting the secondsurface 108 of the material layer 102. The contact (e.g., based onpressure) of the input object 112 on the touch surface defines one ormore contact areas 118 and an amount of reflection. Thresholds can beset based on the contact area 118 of touch for triggering the button andimpedance difference between input object 112 and material layer 102.

The size of the contact areas 118 and space between the contact areas118 can be indicative of the size and spacing of the finger's ridges, aswell as the size and spacing of the valleys of the finger's fingerprint.Certain changes in the size and/or spacing between contact areas 118 canbe indicative of different fingers contacting the material layer 102.For example a young individual may have smaller valleys (e.g., a smallerdistance between contact areas 118) than an older individual. In somecases, the detected size and/or spacing between contact areas 118 can beused to detect or make an inference as to the user contacting thematerial layer 102. Such an inference can be used to applycustomizations (e.g., have a touch event result in different actions fordifferent users or have different sensing thresholds for differentusers), test for permissions (e.g., allow an action only if a recognizeduser is initiating the touch event), or perform other rule-based actionsusing the inference.

The heavy touch 124 can be distinguished from the light touch 122 bydetermining that fewer reflected signals or fewer non-attenuated signalare received by the transducer 104 due to an increased number ofabsorbed ultrasonic signals 116. The ultrasound input device 100 andinput object 112 will have a larger contact area 126 if the pressure ofthe touch is increased, e.g., as the contacting surface flattens. Asshown in FIG. 1, the larger contact area 126 increases the number ofabsorbed ultrasonic signals 116 passing through the second surface 108of the material layer 102 into the input object 112. In the case of auser's finger, the larger contact area 126 can be indicative of a ridgeof the user's finger being flattened against the second surface 108 ofthe material layer 102. In some cases, with the input object 112 is nota finger or is a finger covered by another material, the larger contactarea 126 can be a result of textured elements of the input object 112being flattened against the second surface 108 of the material layer102.

FIG. 2 is a schematic diagram depicting an ultrasound input system in anon-contacted state and a contacted state according to certain aspectsof the present disclosure. FIG. 2 shows the ultrasound input device withno touch 200 (e.g., a non-contacted state) and with a touch 250 (e.g., acontacted state). The ultrasound input device includes a transducer 202coupled to the material layer 204. In this embodiment, the materiallayer 204 is shown as aluminum, but can be any material (e.g., glass,wood, leather, plastic, etc.). The transducer 202 is coupled to a first(interior) surface 206 of the material layer 204. A second (exterior)surface 208 of the material layer 204 is in contact with the air.

For the ultrasound input device with no touch 200, the transducer 202emits an ultrasonic signal 210A directed into the material layer 204 andtoward the second surface 208. Air has an acoustic impedance ofapproximately zero and causes the second surface 208 to reflect areflected ultrasonic signal 212A with close to 100% of the emittedultrasonic signal (e.g., at or more than 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%,99.8%, 99.81%, 99.82%, 99.83%, 99.84%, 99.85%, 99.86%, 99.87%, 99.88%,99.89%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%,99.98%, and/or 99.99%.). The reflected ultrasonic signal 212A can itselfbe reflected off the first surface 206 to generate a reflected-emissionsignal 210B, which can be reflected off the second surface 208 to resultin a second reflected ultrasonic signal 212B. As depicted in FIG. 2,four reflected ultrasonic signals 212A, 212B, 212C, 212D generate fourrespective reflected-emission signals 210B, 210C, 210D, 210E. Any numberof reflected ultrasonic signals 212A, 212B, 212C, 212D, 212E andreflected-emission signals 210B, 210C, 210D, 210E can result from aninitial emitted ultrasonic signal 210A until the signals become tooattenuated to be reflected and/or detected. Plot 214 shows a firstamplitude 216 corresponding to the emitted ultrasonic signal 210A and aset of subsequent amplitudes 218A, 218B, 218C, 218D, 218E correspondingto the reflected ultrasonic signals 212A, 212B, 212C, 212D, 212E. Thefirst subsequent amplitude 218A is smaller than the first amplitude 216due to losses in the material layer 204. Each of the remainingsubsequent amplitudes 218B, 218C, 218D, 218E is smaller than theamplitude of the previous subsequent amplitude 218A, 218B, 218C, 218Ddue to losses in the material layer 204.

In some cases, the frequency or frequencies selected for use with theultrasound input device can be selected to achieve a small or minimalattenuation in a non-contacted state, thus achieving a large or maximumnumber of reflected ultrasonic signals. In some cases, the set ofreflected ultrasonic signals 212A, 212B, 212C, 212D, 212E stemming froma single emitted ultrasonic signal 210A can be referred to as a train ofreflected signals. For illustrative purposes, the various reflectedultrasonic signals 212A, 212B, 212C, 212D, 212E and reflected-emissionsignals 210B, 210C, 210D, 210E are depicted spaced apart from left toright in FIG. 2, however it will be understood that these signals aretemporally separated and may not necessarily be spatially separated.

For the ultrasound input device with a touch 250, an input object 220,in this case a finger, is in contact with the second surface 208 of thematerial layer 204. Reflection loss depends on how much the touch inputmedium versus the input object differ in terms of acoustic impedance.For example, reflection loss (dB) can be represented as 20 log1−(Z2−Z1/Z2+Z1), where Z1 is the impedance of the material layer 204 andZ2 is the impedance of the input object 220. Once an input object 220 isin contact with material layer 204, the emitted ultrasonic signal 210Ais divided into two parts. One part, the echo, consists of a reflectedultrasonic signal 213A and is reflected back towards the transducer. Asecond part 222 penetrates into the input object 220. The reflectedultrasonic signal 213A can itself be reflected off the first surface 206to generate a reflected-emission signal. The reflected-emission signalcan itself be divided into two parts, one of which is a second reflectedultrasonic signal 212B and another of which is the second part 222 thatpenetrates into the input object 220. As depicted in FIG. 2, fourreflected ultrasonic signals 213A, 213B, 213C, 213D generate fourrespective reflected-emission signals. Any number of reflectedultrasonic signals 212A, 212B, 212C, 212D, 212E and reflected-emissionsignals can result from an initial emitted ultrasonic signal 210A untilthe signals become too attenuated to be reflected and/or detected.

As shown by plot 224, a first amplitude 226 corresponds to the emittedultrasonic signal 210A. The first subsequent amplitude 228Acorresponding to reflected ultrasonic signal 213A is reduced compared tothe no touch ultrasound input device due to the second part 222penetrating the input object 220. Each of the remaining subsequentamplitudes 228B, 228C, 228D, 228E is smaller than the amplitude of theprevious subsequent amplitude 228A, 228B, 228C, 228D due to losses inthe material layer 204. For illustrative purposes, plot 224 depicts thesubsequent amplitudes 228A, 228B, 228C, 228D, 228E in solid lineoverlaid with the corresponding subsequent amplitudes 218A, 218B, 218C,218D, 218E in dotted lines. The amount of overall attenuation of thesubsequent amplitudes 228A, 228B, 228C, 228D, 228E of the ultrasoundinput device in a contacted state may be greater than that of thesubsequent amplitudes 218A, 218B, 218C, 218D, 218E of the ultrasounddevice in a non-contacted state. Additionally, the amount of attenuationbetween each of the subsequent amplitudes 228A, 228B, 228C, 228D, 228Eof the ultrasound input device in a contacted state may be greater thanthat of the subsequent amplitudes 218A, 218B, 218C, 218D, 218E of theultrasound device in a non-contacted state.

Of note, the subsequent amplitudes 228A, 228B, 228C, 228D, 228E fromplot 224 that are associated with a touch event attenuate faster thanthe corresponding subsequent amplitudes 218A, 218B, 218C, 218D, 218Efrom plot 214 that are associated with no touch event. In other words,the contrast between subsequent amplitudes of a touch event andsubsequent amplitudes of a no touch event is greater with eachsubsequent reflection number n. In some cases, the ratio of a the n-thsubsequent amplitude associated with no touch event to the n-thsubsequent amplitude associated with a touch event can be Γ^(n):(1−Γ^(n)) where Γ is the percentage of the signal reflected back fromthe second surface 208. For example, the ratio of subsequent amplitude218A to subsequent amplitude 228A may be 100:90; the ratio of subsequentamplitude 218B to subsequent amplitude 228B may be 100:81; the ratio ofsubsequent amplitude 218C to subsequent amplitude 228C may be 100:72;the ratio of subsequent amplitude 218D to subsequent amplitude 228D maybe 100:63; and the ratio of subsequent amplitude 218E to subsequentamplitude 228E may be 100:54.

B. Ultrasound Touch Input Device

FIG. 3 shows an ultrasound input device according to certain aspects ofthe present disclosure. Ultrasound input device 300 can be attached toany surface to detect touch inputs.

The ultrasound input device 300 can include a sensor 302, such as apiezoelectric micromachined ultrasonic transducer (PMUT). A PMUTtransducer is a piezoelectric ultrasonic transducer that comprises athin membrane coupled to a thin piezoelectric film to induce and/orsense ultrasonic signals. The sensor 302 can be integrated on anapplication-specific integrated circuit (ASIC), such as CMOS(complementary metal-oxide-semiconductor) ASIC 304 (all-in-one) andformed on a base 306. The ASIC 304 can include electrical circuitsand/or modules usable to perform various processes as disclosed herein,such as various analog and/or digital processing as described withreference to FIGS. 5-20. For example, ASIC 304 can be used to drivesensor 302, detect reflected ultrasonic signals using sensor 302, anddetermine amplitudes associated with the reflected ultrasonic signals(e.g., using various analog technologies such as accumulation andintegration). In some cases, ASIC 304 can optionally determine athreshold value to which the determined amplitudes can be compared tomake a determination about whether or not a touch event has occurred, inwhich case the ASIC 304 can output a signal associated with theoccurrence of the touch event.

In some cases, circuitry of the ASIC 304 can perform certain process inanalog, such as signal rectification, integration, mixing, modification,accumulation, and the like. As used herein, analog circuitry can includeany circuitry capable of performing an action (e.g., rectification,integration, and the like) on an analog signal without first digitizingthe analog signal. In an example, ASIC 304 can include analog circuitrycapable of taking a received ultrasonic signal, rectifying the signal,and integrating at least a portion of the rectified signal to provide anintegrated signal, such as described with reference to FIG. 6. Inanother example, ASIC 304 can include analog circuitry capable of takinga received ultrasonic signal, calculating absolute values of the signal,and accumulating the absolute values to provide an accumulated signal,such as described with reference to FIG. 8. In another example, ASIC 304can include analog circuitry capable of taking a received ultrasonicsignal, squaring the signal through self-mixing, and integrating thesquared signal to provide an integrated signal, such as described withreference to FIG. 9.

In some cases, a different style of ultrasonic transducer can be usedfor sensor 302 instead of a PMUT sensor. In some cases, the ultrasonicsensor can be formed using a deposited layer of piezoelectric material(e.g., aluminum nitride, lead zirconate titanate (PZT), orpolyvinylidene fluoride (PVDF)). In some cases, the ultrasonic sensorcan be a capacitive micromachined ultrasonic transducer (CMUT). In somecases, the ultrasonic sensor can be a resonator array of piezoelectricdevices (e.g., piezoelectric cantilevers or piezoelectric pillars).

The base 306 can be bonded 310 to a flexible printed circuit/printedcircuit board 308 (FPC/PCB) of a larger integrated device such as amobile phone. In some embodiments, a contact area 312 on the sensor 302can be bonded to a base contact 314. As shown, the dimensions ultrasoundinput device 300 can be equal to or less than 1.5 mm×1.5 mm×0.5 mm insize, although other sizes can be used. In some cases, the FPC/PCB 308to which the base 306 is attached can receive information associatedwith the amplitude of detected reflected ultrasonic signals and performsome of the functionality disclosed herein, such as determiningthreshold values and/or determining when a touch event has occurred.However, in some cases, the FPC/PCB 308 simply receives a signalassociated with occurrence of a touch event, and thus does not need toperform further analysis of amplitudes of detected reflected ultrasonicsignals to perform actions based on a touch event.

The ASIC 304 and sensor 302 integration enables small form factor thatleads placement of buttons or other functionality in many space-limitedapplications. For example, smartphone side mechanical buttons can easilybe replaced with the ultrasound input device 300 under casing. Toimplement a touch interface of a system or other suitable functionality,the ultrasound input device 300 can be bonded to a surface 316 using anadhesive 318.

FIG. 4 is a cross-sectional view of two piezoelectric micromachinedultrasonic transducers integrated to a CMOS wafer according to certainaspects of the present disclosure. Device 400 shows a cross-sectionalview of two PMUTs bonded to a CMOS wafer 402 that can be used in anultrasound input device. Each PMUT may be formed on a MEMS wafer 401that is bonded to a CMOS wafer 402. In this way, PMUTs may be coupled tothe requisite processing electronics of the CMOS wafer 402. It will beunderstood that each PMUT may have an active piezoelectric layer 404along with a first electrode 403 and a second electrode 405. The firstelectrode 403 and the second electrode 405 can be electrically coupledto the piezoelectric layer 404.

In some embodiments, the PMUTs may include a first contact 422electrically coupled to the first electrode 403, a second contact 424electrically coupled to the second electrode 405, and a third electrode426 electrically coupled to the CMOS wafer 402. Applying alternatingvoltage through the first electrode 403 and the second electrode 405 cancause movement (e.g., flexural motion) of the piezoelectric layer 404,which can result in generated sound waves. Likewise, received soundwaves that induce movement in the piezoelectric layer 404 can be sensedas changing voltages across the first electrode 403 and second electrode405. One or more vias 410 may be formed to in the PMUTs. Each of thecontacts may be wire bonded to an electronics board. In someembodiments, PMUTs may include a passivation layer 428 formed on asurface 420 and the contacts. The surface 420 or an adhesive couplingsurface 430 on the surface of the passivation layer 428 may be coupledto a material layer of an ultrasound input device.

In some embodiments, the passive electrical layer 408 may comprise SiO₂or any other suitable passive layer. The active piezoelectric layer 404may be approximately 1 μm thick Aluminum Nitride, and the passiveelastic layer may be approximately 1 μm thick single-crystal Silicon,although other sizes and materials may be used. In some embodiments, theactive piezoelectric layer 404 may be Scandium-doped Aluminum Nitride.Alternatively, the active piezoelectric layer 404 may be anothersuitable piezoelectric ceramic such as PZT. Both the top and bottomelectrodes 406 may comprise Molybdenum. In order to bond the PMUTs tothe top metal 412 of CMOS wafer 402, fusion bonding via thru-silicon-via(TSV) as shown at 410 may be used. This methodology results insignificant parasitic reduction which in turn results in improved signalintegrity and lower power consumption.

In some embodiments, cavity 414 may be formed with a vacuum or nearvacuum to isolate the transducer from the processing electronics in theCMOS wafer 402. The sound generated by the PMUTs will not travel throughthe near vacuum of cavity 414 minimizing reflection and interferencethat may be caused by material interfaces with the CMOS wafer 402. Thecavity 414 may cause ultrasound 416 to travel away from the PMUTs.Ultrasound 416 may travel through the adhesive coupling interface 430and into the material layer of the ultrasound input device. The materiallayer may reflect ultrasound 416 causing a return echo to reflect backto the PMUTs. The return echo travels through the adhesive couplinginterface and is received by the PMUTs.

In some embodiments, the CMOS wafer 402 may be an application specificintegrated circuit (ASIC) that includes one or more devices necessary todrive the transducer. The drive voltage for an array of PMUTs may beless than 4 volts. In some cases, the drive voltage may be less than 1.8volts. In some cases, the drive voltage may be at or less than 4, 3.5,3, 2.5, 2, 1.9, 1.8, 1.7, 1.6, or 1.5 volts. The ASIC can bemanufactured to meet size requirements associated with the size of anassociated PMUT. In some embodiments, the ASIC may include one or moremodules to receive measured signals. The ASIC may be configured tofurther process the signal. For example, the ASIC may include one ormore rectifiers to generate an absolute value signal by taking theabsolute value of the received signals, which may be an alternatingcurrent. The ASIC may also include an integrator and analog to digitalconverters (ADCs) to convert the reflected ultrasonic signal to adigital representation of the reflected signal. The integration of ASICand PMUTs further allows for embedding gain amplifiers and ADC in anASIC and eliminating the standalone ADC-sensor controller chip. Thisopens up space on associated circuit boards and reduces touch inputsensor implementation cost. In some embodiments, the ASIC may transmitthe digital signal to at least one or more of a memory, a processor, anda remote device. In other embodiments, the ASIC may include one or moresignal processing modules.

The PMUT arrays can be compatible with CMOS semiconductor processes. Insome embodiments, PMUT materials and dimensions can be compliant withSemiconductor Equipment and Materials International (SEMI) standardspecifications. Because PMUTs can be compliant with SEMI specifications,the transducer arrays can be used with existing CMOS semiconductorfabrication tools and methods. For example, photolithography may be usedto form one or more PMUTs. In contrast, current piezoelectric ultrasoundtransducer arrays are formed using a die saw that cannot match theprecision of photolithography. As a result, PMUTs can be smaller,operate at lower voltages, and have lower parasitics.

II. Ultrasound Signal Processing

Reflected ultrasonic signals can be processed to produce images anddetermine a range to an object. Embodiments described herein can processreflected ultrasonic signals to determine if an object is in contactwith a surface.

A. Detecting Touch Input by Digitizing Reflected Signal

FIG. 5 is a schematic diagram of a flow 500 for processing ultrasoundsignals emitted and received by an ultrasound input device according tocertain aspects of the present disclosure. The flow 500 includesemitting and receiving an ultrasonic signal as illustrated in a firstplot 502. The first plot 502 shows an analog measurement of a firstsignal 503 for an emitted ultrasonic signal and a set of subsequentsignals 504A, 504B, 504C, 504D, 504E for a set of reflected ultrasonicsignals associated with an ultrasound input device. The first signal 503and the subsequent signals 504 can be measured using a high-speed ADC506 to digitize the signal.

The output of the high-speed ADC 506 is shown in a second plot 508. Thesecond plot 508 includes a first digital representation 510 of theemitted ultrasonic signal and a subsequent digital representations 512A,512B, 512C, 512D, 512E of the reflected ultrasonic signals associatedwith the ultrasound input device. The first digital representation 510and the subsequent digital representations 512A, 512B, 512C, 512D, 512Ecan be processed by a digital processing module in 514 embedded in theultrasound input device and/or a system coupled to the ultrasound inputdevice. The digital processing module 514 can demodulate the digitalrepresentations of the data to extract touch input information. Forexample, the digital processing module can process one or more of thesubsequent digital representations 512A, 512B, 512C, 512D, 512E todetermine that an amplitude of the second digital representation isbelow a threshold value that is associated with an object being incontact with the surface of the ultrasound input device.

B. Detecting Touch Input Using Energy Integration

FIG. 6 is a schematic diagram of a flow 600 for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration according to certain aspects of the present disclosure. Theflow 600 includes emitting and receiving an ultrasonic signal asillustrated in a first plot 602. The first plot 602 shows an analogmeasurement of a first signal 603 for an emitted ultrasonic signal and aset of subsequent signals 604A, 604B, 604C, 604D, 604E for a set ofreflected ultrasonic signals associated with an ultrasound input device.The flow 600 can include an ultrasound input device with an analogcircuit including a rectifier 606 to rectify the subsequent signals604A, 604B, 604C, 604D, 604E.

A second plot 608 shows the first signal 603 and a set of rectifiedsignals 610A, 610B, 610C, 610D, 610E each corresponding to respectiveones of the set of reflected ultrasonic signals. The rectified signals610A, 610B, 610C, 610D, 610E can be processed by an analog integrator612 to output a direct current (DC) signal 613, shown in a third plot614, which is directly proportional to an amplitude of the reflectedultrasonic signal. The DC signal 613 can be determined using an energymeasurement window 616. The DC signal 613 can represent an energy valueassociated with the energy of the received signal measured during theenergy measurement window 616. The DC signal 613 can be processed by alow-speed ADC 618. The DC signal 613 output by the rectifier 606 and theintegrator 612 remove the need to generate a high frequency digitaloutput and, as a result, the low-speed ADC can use less power and can befabricated on a smaller chip area.

FIG. 7 is a schematic diagram of an example of a flow 700 for processingultrasound signals emitted and received by an ultrasound input deviceusing energy integration according to certain aspects of the presentdisclosure. The flow 700 includes emitting and receiving an ultrasonicsignal as illustrated in a first plot 702. The first plot 702 shows ananalog measurement of a first signal 703 for an emitted ultrasonicsignal and a set of subsequent signals 704A, 704B, 704C, 704D, 704E fora set of reflected ultrasonic signals associated with an ultrasoundinput device. The flow 700 can include an ultrasound input device withan analog summation or integration circuit 720 and a summed voltageoutput 722.

A second plot 708 shows the first signal 703 and a set of energy signals710A, 710B, 710C, 710D, 710E each corresponding to the energy ofrespective ones of the set of reflected ultrasonic signals. Forillustrative purposes, the set of energy signals 710A, 710B, 710C, 710D,710E is depicted in solid line overlaid with the set of subsequentsignals 704A, 704B, 704C, 704D, 704E from plot 702 shown in dotted line.

A summation or integration circuit 720 can received the set of energysignals 710A, 710B, 710C, 710D, 710E from within an energy measurementwindow 716. The summation or integration circuit 720 can generate avoltage output 722 that is an analog value representing thesummed/integrated energy within the energy measurement window 716.

In some cases, an optional negative DC charge circuit 724 can be appliedto the summation or integration circuit 720 to offset information notassociated with a touch event. Since touch events are identified basedon differences between received signals during a non-contacting stateand received signals during a contacting state, there is some amount ofinformation within the set of subsequent signals 704A, 704B, 704C, 704D,704E that is not associated with those differences (e.g., a baselinesignal). Removing such baseline signals can result in more effectiverange to sample during analog-to-digital conversion. Since removing sucha baseline signal in analog in the set of subsequent signals 704A, 704B,704C, 704D, 704E would require precise phase alignment, it can bedifficult to apply such corrections. However, as depicted in FIG. 7, andoptional negative DC charge circuit 724 applied to the summation orintegration circuit 720 can offset a particular amount of energyassociated with the baseline signal or a portion thereof, thus improvingthe amount of effective range available for analog-to-digitalconversion. In such cases, the voltage output 722 can be proportional tothe energy of the signal minus the energy of the negative DC chargecircuit 724.

The voltage output 722 can be processed by a low-speed ADC 718. Thevoltage output 722 of the summed/integrated energy within the energymeasurement window 716 can remove the need to generate a high frequencydigital output and, as a result, the low-speed ADC can use less powerand can be fabricated on a smaller chip area.

FIG. 8 is a schematic diagram of a flow 800 for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration via absolute value accumulation according to certain aspectsof the present disclosure. Flow 800 can be one technique forimplementing flow 700 of FIG. 7. The flow 800 includes emitting andreceiving an ultrasonic signal as illustrated in a first plot 802. Thefirst plot 802 shows an analog measurement of a first signal for anemitted ultrasonic signal and a set of subsequent signals for a set ofreflected ultrasonic signals associated with an ultrasound input device.The first plot 802 can depict voltage as a function of time (e.g.,V(t)). The first plot 802 can be first plot 702 of FIG. 7. The flow 800can include an ultrasound input device with an analog sampling circuit806, and absolute value circuit 814, an analog accumulator 824, and asummed voltage output 828.

The set of subsequent signals from plot 802 can be passed through ananalog sampling circuit 806 to result in a sampled first signal 810 anda set of sampled subsequent signals 812A, 812B, 812C, 812D, 812E asdepicted in second plot 808. The second plot 808 can depict voltage as afunction of sample (e.g., V(n) where n is the sample number). Thesampled subsequent signals 812A, 812B, 812C, 812D, 812E can be passed toan absolute value circuit 814 that can generate a set of energy signals820A, 820B, 820C, 820D, 820E as depicted in third plot 816. The thirdplot 816 can depict an absolute value of voltage as a function of sample(e.g., |V(n)|). The absolute value circuit 814 can pass all zero orpositive values of the set of sampled subsequent signals 812A, 812B,812C, 812D, 812E and reverse the polarity of all negative values.

A switch-capacitor analog accumulator 824 can be used to sum the set ofenergy signals 820A, 820B, 820C, 820D, 820E from within the energymeasurement window 822. The switch-capacitor analog accumulator cangenerate a voltage output 828 that is an analog value representing thesum of the energy within the energy measurement window 822. In somecases, an analog integrator can be used instead of an accumulator.

In some cases, an optional negative clocked DC charge circuit 826 can beapplied to the switch-capacitor analog accumulator 824 to offsetinformation not associated with a touch event. Since the samplingcircuit 806 is clocked according to a sample rate, the optional negativeclocked DC charge circuit 826 can be clocked at the same rate to ensurethe biasing voltage is applied at the appropriate intervalscorresponding to the samples of the sampled subsequent signals 812A,812B, 812C, 812D, 812E. When an optional negative clocked DC chargecircuit 826 is used, the voltage output 828 can be proportional to theenergy of the signal minus the energy of the negative clocked DC chargecircuit 826.

The voltage output 828 can be processed by a low-speed ADC 830. Thevoltage output 828 of the summed energy within the energy measurementwindow 822 can remove the need to generate a high frequency digitaloutput and, as a result, the low-speed ADC can use less power and can befabricated on a smaller chip area.

FIG. 9 is a schematic diagram of a flow 900 for processing ultrasoundsignals emitted and received by an ultrasound input device using energyintegration via self-mixing and integration according to certain aspectsof the present disclosure. Flow 900 can be one technique forimplementing flow 700 of FIG. 7. The flow 900 includes emitting andreceiving an ultrasonic signal as illustrated in a first plot 902. Thefirst plot 902 shows an analog measurement of a first signal for anemitted ultrasonic signal and a set of subsequent signals for a set ofreflected ultrasonic signals associated with an ultrasound input device.The first plot 802 can depict voltage as a function of time (e.g.,V(t)). The first plot 902 can be first plot 702 of FIG. 7. The flow 900can include an ultrasound input device with a self-mixing circuit 906,an analog integrator circuit 920, and an integrated voltage output 926.

The set of subsequent signals from plot 902 can be passed through theself-mixing circuit 906 to generate a set of squared subsequent signals910A, 910B, 910C, 910D, 910E as depicted in the second plot 908. Theself-mixing circuit 906 can effectively multiply every analog value byitself over time. As a result, the second plot 908 can depict squaredvoltage as a function of time (e.g., V²(t)). Due to the nature ofsquares, and thus the nature of self-mixing circuit 906, the set ofsquared subsequent signals 910A, 910B, 910C, 910D, 910E will always bepositive.

The set of squared subsequent signals 910A, 910B, 910C, 910D, 910E canbe passed to an analog integrator circuit 920. The analog integratorcircuit 920 can integrate the set of squared subsequent signals 910A,910B, 910C, 910D, 910E within the energy measurement window 916 togenerate an integrated voltage output 922. The integrated voltage output922 can be an analog representation of the total energy within theenergy measurement window 916 over time. In some cases, an accumulatorcan be used instead of an analog integrator circuit 920.

In some cases, an optional negative bias current circuit 924 can beapplied to the analog integrator circuit 920 to offset information notassociated with a touch event. The negative bias current circuit 924 canconstantly drain charge out of the analog integrator circuit 920 duringintegration. When an optional negative bias current circuit 924 is used,the voltage output 922 can be proportional to the energy of the signalminus the energy of the negative bias current circuit 924.

The voltage output 922 can be processed by a low-speed ADC 930. Thevoltage output 922 of the integrated energy within the energymeasurement window 916 can remove the need to generate a high frequencydigital output and, as a result, the low-speed ADC can use less powerand can be fabricated on a smaller chip area.

FIG. 10 is a schematic circuit diagram depicting an analog integrator1000 with a negative bias current according to certain aspects of thepresent disclosure. The analog integrator 1000 negative bias can be theanalog integrator circuit 920 and optional negative bias current circuit924 of FIG. 9.

The analog integrator 1000 can receive an input voltage (V_(in)) througha resistor (R_(in)) to obtain an input current (I_(in)). A capacitor (C)can be charged by a charging current (I_(f)) to generate the integratedsignal, which can feed the voltage output (V_(out)). Item (A) is anop-amp. A negative biasing current (I_(bias)) can be applied at point Xto drain charge out of the analog integrator 1000, thus resulting in areduced charging current (I_(f)). Therefore, the charging current can becalculated as I_(f)=I_(n)−I_(bias).

C. Energy Measurement Windowing

FIG. 11 is a schematic diagram of a flow for processing ultrasoundsignals depicting the reduced effects of time-of-flight changes on touchinput detection within an energy measurement window according to certainaspects of the present disclosure. In an ultrasound imaging system orproximity detection system, an accurate time-of-flight is critical todetermine the distance of objects in a field of view from an ultrasonictransducer. In contrast with imaging and proximity systems, the distanceto the first and second surface of the material layer in the ultrasoundinput device can be provided and a touch input can be detected withoutaccounting for changes in time-of-flight. FIG. 11 shows a first plot1102 where a first set of reflected ultrasonic signals 1104 is receivedstarting at a first time 1106 and a second plot 1108 where a second setof reflected ultrasonic signals 1110 is received at a second time 1112.The first set of reflected ultrasonic signals 1104 is passed through anenergy accumulator or integrator circuit 1120 to generate an outputvoltage 1122 (e.g., V_(sum1)) that can be fed into a low-speed ADC 1124and processed to obtain an output value 1118 (e.g., 3000 LSB where LSBstands for least-significant bit). The second set of reflectedultrasonic signals 1110 is passed through an energy accumulator orintegrator circuit 1120 to generate an output voltage 1123 (e.g.,V_(sum2)) that can be fed into a low-speed ADC 1124 and processed toobtain an output value 1119 (e.g., 3000 LSB where LSB stands forleast-significant bit). The output values 1118, 1119 can berepresentative of the pulse reflection energy during the energymeasurement windows 1116 of plots 1102, 1108. Despite the differentstarting times of the first set of reflected ultrasonic signals 1104 andthe second set of reflected ultrasonic signals 1110 (e.g., first time1106 and second time 1112), the output values 1118, 1119 can be the sameor substantially the same since the entire first set of reflectedultrasonic signals 1104 and entire second set reflected ultrasonicsignals 1110 each fit within the energy measurement window 1116.

Thus, the ultrasonic input device can be insensitive to time-of-flight,at least to a degree (e.g., within the energy measurement window). Insome cases, advanced windowing techniques, such as those disclosedherein, can further improve the ultrasonic input device's insensitivityto time-of-flight. As a result, the surface of the ultrasonic inputdevice (e.g., material layer)_need not be entirely flat and/or thealignment of the ultrasonic input device against a material (e.g.,material layer) need not be exactly at 90° (e.g., the angle between thepropagation direction of the ultrasonic transducer and the surface ofthe material layer). Further, the insensitivity to time-of-flight canpermit some insensitivity to varying indexes of refraction through whichthe ultrasonic signals pass (e.g., a material layer having somewhatinconsistent indices of refraction throughout).

As shown in FIGS. 6-9 and 11, the energy of the reflected ultrasonicsignals (e.g., reflected echoes and standing waves) is summed orintegrated over an energy measurement window. This energy is correlatedto the condition of a touch input and thus can be used for input touchdetection. The energy measurement window 1116 can be sized to includethe pulse time of the ultrasonic signal and account for changes in thetime-of-flight due to temperature, stack variations (e.g., variations inthe materials making up the ultrasonic input device), etc. The energymeasurement window 1116 can reduce errors due to variations in thetime-of-flight. The ultrasonic touch device can determine input touchcontact based on a specific threshold.

FIG. 12 is a schematic diagram of an abbreviated flow for processingultrasound signals depicting the heightened effects of reflectedultrasonic signal time-of-flight changes on touch input detectionoutside of an energy measurement window. FIG. 12 shows a first plot 1202where a first set of reflected ultrasonic signals 1204 is receivedstarting at a first time 1206 and a second plot 1208 where a second setof reflected ultrasonic signals 1210 is received at a second time 1212.The first set of reflected ultrasonic signals 1204 is passed through anenergy accumulator or integrator circuit 1220 to generate an outputvoltage 1222 (e.g., V_(sum1)) that can be fed into a low-speed ADC 1224and processed to obtain an output value 1218 (e.g., 3000 LSB where LSBstands for least-significant bit). The second set of reflectedultrasonic signals 1210 is passed through an energy accumulator orintegrator circuit 1220 to generate an output voltage 1223 (e.g.,V_(sum2)) that can be fed into a low-speed ADC 1224 and processed toobtain an output value 1219 (e.g., 2500 LSB where LSB stands forleast-significant bit). The output values 1218, 1219 can berepresentative of the pulse reflection energy during the energymeasurement windows 1216 of plots 1202, 1208.

As depicted in FIG. 12, because nearly all of the first set of reflectedultrasonic signals 1204 fits within the energy measurement window 1216,but a smaller portion of the second set of reflected ultrasonic signals1210 fits within the energy measurement window 1216, output value 1218is greater than output value 1219. As depicted in FIG. 12, the outputvalues 1218, 1219 differ by 500 LSB. If the reflected ultrasonic signalsfall outside of the energy measurement window 1216, some of the measuredpulses may be cut off from being measured and thus the ultrasonic inputdevice may be susceptible to time-of-flight variations (e.g., variationsthat would cause a difference in first time 1206 and second time 1212).

FIG. 13 is a schematic diagram of a flow for processing ultrasoundsignals depicting the minimal effects of reflected ultrasonic signaltime-of-flight changes on touch input detection outside of an energymeasurement window when window shaping is used according to certainaspects of the present disclosure. FIG. 13 shows a first plot 1302 wherea first set of reflected ultrasonic signals 1304 is received starting ata first time 1306 and a second plot 1308 where a second set of reflectedultrasonic signals 1310 is received at a second time 1312. The first setof reflected ultrasonic signals 1304 is passed through an energyaccumulator or integrator circuit to generate an output voltage (e.g.,V_(sum1)) that can be fed into a low-speed ADC and processed to obtainan output value 1318 (e.g., 2500 LSB where LSB stands forleast-significant bit). The second set of reflected ultrasonic signals1310 is passed through an energy accumulator or integrator circuit togenerate an output voltage (e.g., V_(sum2)) that can be fed into alow-speed ADC and processed to obtain an output value 1319 (e.g., 2450LSB where LSB stands for least-significant bit). The output values 1318,1319 can be representative of the pulse reflection energy during theenergy measurement windows 1316 of plots 1302, 1308.

Unlike FIG. 12, an energy measurement window envelope 1320 is used inconjunction with the energy measurement window 1316. The energymeasurement window envelope 1320 scales portions of the signal withinthe energy measurement window 1316 such that portions near the edges ofthe energy measurement window 1316 are given less weight than portionsnear the center of the energy measurement window 1316. Thus, despitesmall variations near the ends of the energy measurement window 1316,the resultant output values will be mostly based on the signals measuredwithin the center of the energy measurement window 1316. The energymeasurement window envelope 1320 is depicted in FIG. 13 as having aparticular flared bell shape, although any suitable shape can be used,including symmetrical and non-symmetrical shapes. The vertical extent ofthe energy measurement window envelope 1320 as depicted in FIG. 13 canrepresent any suitable scale, such as 0% to 100%. In some cases, theenergy measurement window envelope 1320 can include amplifying signalsnear the center of the energy measurement window 1316, such as to valuesabove 100% of the original signal at that time.

As depicted in FIG. 13, because of the use of an energy measurementwindow envelope 1320, the signals (e.g., first set of reflectedultrasonic signals 1304 and second set of reflected ultrasonic signals1310) are weighted so the portions of the signals nearest the center ofthe energy measurement window 1316 are given more weight than theportions nearest the edges of the energy measurement window 1316, thusde-emphasizing any portions cut off by the start or end of the energymeasurement window 1316. As a result, the output values 1318, 1319 aremuch closer than output values 1218, 1219 of FIG. 12. As depicted inFIG. 13, the output values 1318, 1319 only differ by 50 LSB. Thus, as aresult of an energy measurement window envelope 1320, the ultrasonicinput device can become less susceptible to time-of-flight variations.

FIG. 14 is a schematic circuit diagram depicting a window shapingcircuit 1400 according to certain aspects of the present disclosure. Thewindow shaping circuit 1400 can generate an energy measurement windowhaving an energy measurement window envelope (e.g., energy measurementwindow 1316 having energy measurement window envelope 1320 of FIG. 13).The window shaping circuit 1400 can operate as a traditional analogaccumulator circuit with the addition of an adjustable capacitor 1402.The adjustable capacitor 1402 can take any suitable form, such as aswitched ladder of different sized capacitors. The choice of capacitorsize for adjustable capacitor 1402 over time can result in an adjustmentof gain on the analog accumulator circuit over time. In some cases, theadjustable capacitor 1402 can be driven by a clock 1404 or other sourceto determine when to chance capacitance. In some cases, the adjustablecapacitor 1402 can be used with an analog sampling circuit, such asanalog sampling circuit 806 of FIG. 8, and the adjustable capacitor 1402can be changed with different sample numbers (e.g., n of V(n)).

FIG. 15 is a schematic diagram depicting a flow 1500 for processingultrasound signals to detect a touch input using the amplitude ofreflected ultrasonic signals according to certain aspects of the presentdisclosure. FIG. 15 shows an ultrasound input device 1502 with no touchinput 1504 and with a touch input 1506. A first plot 1508 associatedwith the ultrasound input device 1502 with no touch input 1504 shows atransmitted signal 1510 and a first set of reflected signals 1512. Thefirst set of reflected signals 1512 can be processed, as disclosedherein, to generate an output voltage 1530 (e.g., V_(sum1)), which canbe provided to a low-speed ADC 1534 and further processed to generate afirst output 1536. The first output 1536 can be representative of theenergy of the first set of reflected signals 1512 within the energymeasurement window 1516. A second plot 1514 shows a transmitted signal1522 and a second set of reflected signals 1512. The second set ofreflected signals 1524 can be processed, as disclosed herein, togenerate an output voltage 1532 (e.g., V_(sum2)), which can be providedto a low-speed ADC 1534 and further processed to generate a secondoutput 1538. The second output 1538 can be representative of the energyof the second set of reflected signals 1524 within the energymeasurement window 1516.

An energy measurement window envelope 1516 (e.g., an envelope similar toenergy measurement window envelope 1320 of FIG. 13) can be applied tothe first set of reflected signals 1512 and the second set of reflectedsignals 1524.

The first output 1536 and the second output 1538 can be compared todetermine whether a touch input (e.g., touch event) has occurred. Forexample, if the second output 1538 is lower than the first output 1536by a predetermined amount and/or if the second output 1538 is lower thana threshold value, the ultrasound input device can generate a signalindicating a touch input is present on a surface. Since the outputvoltages 1530, 1532 are indicative of the first output 1536 and secondoutput 1520, respectively, the output voltages 1530, 1532 can be used todetermine whether a touch input has occurred. In some embodiments, onlya single output, such as the first output 1518, can be compared to areference value. The reference value can be established at the time ofmanufacturing and/or be updated based on background characteristicsmeasured by or communicated to the device, such as temperature.

D. Touch Input Error Prevention

FIG. 16 is a chart 1600 depicting reflected ultrasonic signalmeasurements made using an ultrasound input device and illustratingtechniques to improve touch input detection according to certain aspectsof the present disclosure. The sensor readout (e.g., DC signal or othersensor data) determined by the ultrasound input device can be measuredcontinuously or at a specific frequency depending on the application. Insome embodiments, the sensor readout can be measured at a frequency of100 Hz. An individual measurement 1602 can correspond to the energymeasurement within an energy measurement window. One or more individualmeasurements can be used to determine a current state 1606. The currentstate can be defined by the current individual measurement 1602 or by abest-fit line based on two or more individual measurements. In someembodiments, the best-fit line can be calculated using a least-squaresmethod. A plurality of individual measurements can be used to determinea moving average threshold 1604.

The current state 1606 and the moving average threshold 1604 can be usedto detect a touch event. The moving average threshold 1604 can be usedto determine a sudden signal drop that can trigger a touch input event.For example, the system can detect a “hand-touch” effect only if a“rapid signal change” 1608 from a current state 1606 is detected. Arapid signal change 1608 can be associated with a sudden signal drop onall or many channels, and can be considered a touch input event. Athreshold to detect the rapid signal change 1608 can be themoving-average threshold 1604 when no hand-touch event is detected.(Dynamic threshold). In some embodiments, the rapid signal change 1608can be a pre-programmed static threshold. The rapid signal change 1608event can trigger a touch input event and cause the ultrasound inputdevice to generate a signal indicating a touch input on a surface of thedevice. For a rapid signal change 1608 event, multiple measurements 1610are made to ensure signal did actually drop and does not jump back up,such as to its original value. For example, a hard press by a user mayresult in a dropping sensor readout, but will still provide a continuoussignal. During the multiple measurements 1610, if the signal rapidlyreturns to a higher value, such as the value previously seen before thesuspected touch event, the ultrasound input device can recognize thetemporary signal drop as a false touch event and not classify it as atouch event. Multiple measurements 1610 can occur over a very shorttimeframe (e.g., on the order of tens or hundreds of milliseconds). Insome embodiments, a “gradual signal change” can be treated astemperature change but not hand touch event because the moving averagewill adjust with each individual measurement 1602 at a rate based on thenumber of measurements used to determine the moving average.

In some cases, a threshold 1604 can be based on a calculation other thana moving average calculation. In some cases, the threshold 1604 issimply some function of past history (e.g., historical measurements),such as a function of the past x number of measurements. In some cases,past measurements can be weighted, such as more recent measurementsbeing weighted higher than measurements taken longer ago. In such cases,the response time of the ultrasonic input device can be adjusted basedon the weightings of the past x measurements. For example, a thresholdcan be calculated as a function of historical values according toThreshold=f(X[n−1], X[n−2], . . . , X[n−m]) where X[n] is the n-thsensor readout (or the current sensor readout). In another example, thethreshold can be calculated as a function of weighted historical valuesaccording to Threshold=w₁X[n−1]+w₂X[n−2], . . . , w_(m)X[n−m] wherew_(n) is a weighting parameter for the n-th sensor readout. In somecases, weighting parameters can be trained using machine learning, suchas described in further detail herein.

In some cases, in addition to or instead of determining a rapid signalchange 1608 based on measurements themselves, the determination can bemade using a slope of a set of measurements, such as a slope of thecurrent measurement and some number of past measurements.

FIG. 17 is a chart 1700 depicting reflected ultrasonic signalmeasurements made using an ultrasound input device and illustratingadditional techniques to improve touch input detection according tocertain aspects of the present disclosure. A portion of chart 1700 isdepicted as chart 1600 of FIG. 16. Chart 1700 shows that signalvariation over time may occur due to various factors, such astemperature changes, however the ultrasonic input device may be able todiscern that these variations are not touch events. However, suddensignal drops between consecutive measurements can be indicative of atouch event. Current state 1706 can be similar to current state 1606 ofFIG. 16. The moving average threshold 1704 can be similar to threshold1604 of FIG. 16. This threshold 1704 can be based in part on a movingaverage of previous measurements of the current state 1706, such as amoving average of previous measurements offset by a given amount. Thistype of threshold 1704 can be known as a dynamic threshold, althoughother threshold techniques can be used.

At region 1716, a touch event occurs. When the touch event occurs, thecurrent state 1706 quickly drops. As depicted in the callout portion ofchart 1700, various measurements 1702 are shown. Each measurement 1702can be separated in time based on a measurement frequency. For example,each measurement 1702 can be 0.01 seconds apart (e.g., at 100 Hz),although other frequencies can be used. A sudden drop can be detectedbetween two or more consecutive measurements 1702. When the sudden dropin current state 1706 falls below the threshold 1704, a touch event canbe considered to have occurred. Region 1717 depicts another touch event.

At region 1718 and region 1720, gradual changes in temperature of theultrasonic sensor and surface to which the sensor is coupled can resultin gradual changes in current state 1706. Because of the relatively slowchanges in the current state 1706, the threshold 1704, which is based ona moving average of the current state 1706, will make changes as well.Since the threshold 1704 is able to compensate for slow changes in thecurrent state 1706, such as those that occur due to temperature changes,these slow changes in current state 1706 do not pass the threshold 1704and therefore do not trigger touch events. Furthermore, since thethreshold 1704 is dynamically updating, the threshold 1704 is able tooperate properly at different temperatures. In some cases, changes incurrent state 1706 due to temperature variation can be even larger thancontrast resulting from an actual hand touch, but since thesetemperature variations are much slower than the changes in current state1706 due to a touch event, they are not detected as touch events.

III. Multifrequency Touch Detection

FIG. 18 is a chart depicting a temperature dependence of reflectedultrasonic signals according to certain aspects of the presentdisclosure. The reflected ultrasonic signals received by an ultrasoundinput device can include the main signal 1802 and any unwanted signals1804. The main signal travels a first path through the material layerand is associated with a first time-of-flight (TOF) and any unwantedsignals 1804 travel a second path through the material layer and areassociated with a second TOF. The speed of sound in a material layerdepends on the temperature of the material layer. Due to speed of soundchanges as a result of temperature changes, the main signal 1802 and theunwanted signals 1804 travel through different acoustic paths, and theassociated first TOF and second TOF change a different amountaccordingly. This creates a net TOF difference Δt(T) 1806 between themain signal 1802 and the unwanted signal 1804 which change withtemperature T. This then translates into a phase delay difference Δϕ(T)between the main signal 1802 and the unwanted signal 1804. And thusyields different integrated signal strength difference Dout(T) asdepicted by line 1810.

FIG. 19 is a set of charts depicting TOF temperature dependence of a twofrequency method of detecting a touch input according to certain aspectsof the present disclosure. The charts can be similar to the charts ofFIG. 18. In a multi-frequency ultrasound input device, differentfrequencies will have different temperature effects resulting in adifferent TOF for each signal. The multi-frequency ultrasound inputdevice can process a “finger touch” (e.g., touch event) when a signaldrop is detected in a threshold number of frequency channels. Forexample, two different methods can detect whether a finger touched theultrasound touch input device, and the device can only process the touchevent when both of the methods agree finger touch has been detected.

In a multi-frequency ultrasound touch input device, a first signal 1902at a first frequency and a second signal 1904 at a second frequency havedifferent background and temperature drift characteristics. For example,the first signal 1902 and the second signal 1904 experience the sameΔt(T) when temperature changes. As a result of the different temperaturedrift characteristics, the same Δt(T) will translate to a differentphase delay for each frequency. For example, the first signal 1902 willhave a first phase delay of Δϕ↓1(T) 1906 and the second signal 1904 willhave a second phase delay Δϕ↓2(T) 1908. The resulting difference in thephase delay can cause two different ADC output value patterns overtemperature Dout↓1(T) and Doutθ2(T), as depicted by lines 1910, 1912,respectively.

Therefore, signal drop can be measured in multiple frequencies in orderto increase touch detection reliability and reduce false triggerdetection. A touch input event can be processed if all the frequencychannels detect a sudden signal drop. The multiple measurements canoccur very fast (<1 ms) to make sure the sudden signal drop is not dueto temperature effects.

The multi-frequency ultrasound touch input device can avoid falsetriggers by reducing noise associated with environmental conditions. Thetouch input device can immediately execute a rapid pulse-echo test toensure the touch event is real but not a false trigger due to noise. Insome embodiments, the multiple tests can happen within 1 ms.

FIG. 20 is a multi-part chart 2000 depicting reflected ultrasonic signalmeasurements made across several frequencies using an ultrasound inputdevice and illustrating techniques to improve touch input detectionaccording to certain aspects of the present disclosure. Differentfrequencies of ultrasonic signals can exhibit different variation due totemperature changes. Thus, by sensing using multiple ultrasonicfrequencies, the ultrasonic input device can compare a suspected touchevent with the data from one or more other frequencies to ensure thesuspected touch event is confirmed by the one or more other frequencies.The use of multiple frequencies can reduce error rates.

Line 2006 can represent energy signals associated with a 100 kHzfrequency, line 2005 can represent energy signals associated with a 1MHz frequency, and line 2007 can represent energy signals associatedwith a 10 MHz frequency. Line 2004 can represent a moving averagethreshold, such as threshold 1604 from FIG. 16. For illustrativepurposes, a moving average threshold is only depicted with respect tothe 100 kHz frequency, but respective thresholds can exist for eachfrequency used (e.g., 1 MHz and 10 MHz). While the frequencies 100 kHz,1 MHz, and 10 MHz are used with respect to FIG. 20, any other suitablefrequencies can be used. While three different frequencies are used withrespect to FIG. 20, any number of different frequencies, such as two orgreater than three, can be used. A touch event may be registered only ifthe touch event is detected across all, a majority of, or at least athreshold percentage of different frequencies being used for detection.

In some cases, instead of or in addition to driving an ultrasonic inputdevice at different frequencies, the ultrasonic input device can drivean ultrasonic array with different phase delays to generate differentbeampatterns. Since different beampatterns can have differenttemperature characteristics, different beampatterns can be used similarto different frequencies to reduce error and confirm suspected touchevents.

FIG. 21 shows a plan view of a two-frequency PMUT 2100 according tocertain aspects of the present disclosure. In some embodiments, acircular PMUT design can be fabricated to achieve multi-frequencytransducers. The circular PMUT design can consist of multiple individualchannels for transmit and receive per frequency. In some cases, themultiple channels or transducers can be arranged concentrically. Forexample, the two frequency PMUT 2100 includes a first transmit/receivepair 2102 associated with a low frequency. The first transmit/receivepair 2102 can include a low frequency transmit ring 2104 and a lowfrequency receive ring 2106. The two frequency PMUT 2100 also includes asecond transmit/receive pair 2108 associated with a high frequency. Thesecond transmit/receive pair 2108 can include a high frequency transmitring 2110 and a low frequency receive ring 2112. In various embodiments,a circular PMUT design can include a range of multiple frequencies from2 to 10. The range of frequencies can be from 1 MHz to 10 MHz. In someembodiments, frequencies less than 1 MHz can be used depending on thematerial layer and specific application. A second PMUT array can beadded for TOF measurement at the 1-3 MHz range. In some cases, theranges of frequencies used for any array can be from 30 kHz to 50 Mhz.

FIG. 22 is a schematic plan view depicting a multi-frequency ultrasoundinput device 2200 with a square design according to certain aspects ofthe present disclosure. The square sensor design can consist of a squaregrid of multiple individual channels for transmit and receive perfrequency. In some cases, one or more receiving channels can bepositioned between multiple transmitting channels. In such cases, theposition of a receiving channel between multiple transmitting channelscan facilitate receiving and detecting reflected signals. In an example,the multiple-frequency input device 2200 can include variouslow-frequency transmitters 2202, low-frequency receivers 2204,high-frequency transmitters 2206, and high-frequency receivers 2208. Thesquare design can include nested patterns, such as the cross-shapednested pattern depicted in FIG. 22. Any other suitable pattern can beused. The various transmitters and receivers can be any suitablefrequency, such as between 30 kHz to 50 Mhz, 1 Mhz to 10 Mhz, or anyother suitable range.

IV. Machine Learning Decision Algorithm

FIG. 23 is a chart 2300 depicting a machine learning decision algorithmused to improve touch detection according to certain aspects of thepresent disclosure. As described with reference to FIG. 16, weightingparameters can be used to drive various decisions regarding when a touchevent is detected or not detected. In some cases, a machine learningapproach can take into account sensor output values and slopes between asensor value and a previous sensor value to generate inferences that atouch event has occurred or not occurred. The machine learning approachcan use a decision function (f), such as:

f=w ₀ X[n]+w ₁ X[n−1]+w ₂ X[n−2]+ . . . +w _(m) X[n−m]+w _(S0) S[n]+W_(S1) S[n−1]+ . . . +w _(sm) S[n−m]

where w_(n) and w_(sn) are weighting parameters, X[n] is the currentsensor output, X[n−1] is the previous sensor output, X[n−m] is the m-thprevious sensor output, S[n] is the slope of the current sensor output(e.g., as compared to an immediately prior sensor output), S[n−1] is theslope of the previous sensor output, and S[n−m] is the slope of the m-thprevious sensor output. In some cases, other parameters can be used inthe decision function.

The weighting parameters of the decision function can be trained over acorpus of data to generate a decision boundary between inputs that areconsidered touch events and inputs that are not considered touch events,as depicted in chart 2300. Thus, for any given sensor outputs and slopesof sensor outputs, a point on chart 2300 can be identified, and if thatpoint falls above the decision boundary, those sensor outputs and slopesof sensor outputs can be considered indicative of a touch event.

V. Applications

FIG. 24 is a schematic diagram depicting an electronic device with anultrasound input device according to certain aspects of the presentdisclosure. The electronic device 2400 can include a case 2402, a screen2404, one or more front facing buttons 2406, a pair of ultrasound inputdevices 2408, and an individual ultrasound input device 2410. Theelectronic device 2400 can include a processor, memory, and a networkinterface. In some embodiments, the ultrasound input devices can becoupled to the processor of the electronic device 2400.

In some embodiments, the pair of ultrasound input devices 2408 candefine an input touch area 2412 to detect user inputs. For example, auser can contact the input touch area 2412 to adjust the volume, thebrightness, etc. of the electronic device. In some embodiments, an arrayof ultrasound input devices can be positioned under the screen to detecttouch inputs and replace or augment a capacitive touch or force touchcapability of the electronic device. The individual ultrasound inputdevice 2410 can define an input touch area 2414 to detect user inputs.The input touch area 2414 can be configured to control the device power,screen on/off, etc.

In some embodiments, an ultrasound input device can be used to detect atouch input at each of the one or more front facing buttons 2406. Theultrasound input device can replace the capacitive sensing used todetect a touch input on a fingerprint sensor. The ultrasound inputdevice offers a low power solution to detect the touch input on thefingerprint sensor. In some embodiments, one or more ultrasound inputdevices can be positioned under a logo 2422 on the back 2420 of the case2402 to detect user input.

FIG. 25 is a schematic depiction of a steering wheel 2502 with anultrasound input device 2504 according to certain aspects of the presentdisclosure. The ultrasound input device 2504 can be used to form a touchinput area on the steering wheel 2502 to detect a touch input. Theflexibility of the ultrasound input device 2504 facilitates detection ofa touch input through a variety of materials used to manufacture asteering wheel such as plastic, leather, wood, etc. The cross section2506 of the steering wheel 2502 shows the ultrasound input devicecoupled to a surface 2508 to form a touch input area 2510. The touchinput area can be combined with a plurality of touch input areas for aapplications such as cruise control, infotainment input control,cellular communications controls; and driver detection systems. Forexample, the ultrasound input device 2504 can be used in a driverdetection system to determine if a driver's hands are in contact withthe steering wheel.

FIG. 26 is a schematic depiction of a keypad 2600 using an ultrasoundinput device according to certain aspects of the present disclosure. Theshape and materials that can be used to design a touch area withunderlying ultrasound input devices are limited only be the creativityof the designer. For example, a 12-key standard telephone keypad isshown in FIG. 26. The keypad 2600 can include 12 ultrasound inputdevices 2602 to form a touch area 2604 for each key.

FIG. 27 is a schematic diagram depicting a robotic arm using anultrasound input device according to certain aspects of the presentdisclosure. The robotic arm 2700 can include a first finger 2702 and asecond finger 2704. The ultrasound input device can be implemented as arobot finger input device. The first finger 2702 and the second finger2704 can include a first ultrasound input device 2706 and a secondultrasound input device 2708 respectively. The first ultrasound inputdevice 2706 can form a contact area 2710 on the surface of the firstfinger 2702 and the second ultrasound input device 2708 can form asecond contact area 2712 on the second finger. The ultrasound inputdevices improve the detection capability of the robot arm because theycan be integrated into fingers comprising any material. Further, theultrasound input devices can detect a touch input without requiring acutout and/or a different material being integrated into the finger.

FIG. 28 is a schematic diagram depicting a piece of furniture 2802 usingan ultrasound input device 2804 according to certain aspects of thepresent disclosure. The ultrasound input device 2804 can be coupled tothe furniture 2802 in any suitable fashion. A user touching thefurniture 2802 at or adjacent to the location of the ultrasound inputdevice 2804 can be detected by the ultrasound input device 2804 (e.g.,via ultrasound touch sensor 2812). Upon detecting touch, the ultrasonicinput device 2804 can perform any preprogrammed functions. For example,a communication module 2814 of the ultrasonic input device 2804 can senda signal (e.g., a wireless signal) to a control module 2806 spaced apartfrom the ultrasonic input device 2804 and/or the furniture 2802. Thecontrol module 2806 can control another device, such as a power switch2808 coupled to a light bulb 2810. Thus, upon pressing a location on thefurniture 2802 that is at or adjacent to the location of the ultrasoundinput device 2804, the light bulb 2810 can be turned on, be turned off,or otherwise be controlled. The device being controlled (e.g., lightbulb 2810) can be in the same environment as the ultrasound input device2804, although that need not always be the case. In some cases, thedevice being controlled can be in an adjacent environment or even adistant environment.

The ultrasound input device 2804 according to certain aspects of thepresent disclosure can operate on very low power, such as from aninternal battery 2816. This battery-powered, low power operation canpermit use of the ultrasound input device 2804 in otherwise inaccessibleor inconvenient locations. For example, a light switch can beincorporated into a table or desk, or a television remote can beincorporated into an armrest of a chair.

In some cases, an ultrasound input device 2804 can be positioned on ahidden surface 2818 so as to hide the ultrasound input device 2804 fromsight during normal operation. A hidden surface 2818 can be an undersideof a table (e.g., furniture 2802), the inside of a piece of furniture,the inside of a wall, or any other suitable location hidden from view.Thus, the hidden ultrasound input device can be actuated only by thoseknowing its location, which would otherwise be hidden from view.

VI. Additional Piezoelectric Array Designs

FIG. 29 is a schematic diagram of a piezoelectric resonator array 2900containing piezoelectric cantilevers 2902 usable in an ultrasound inputdevice according to certain aspects of the present disclosure. Thepiezoelectric resonator array 2900 can contain a set of piezoelectriccantilevers 2902 on a base 2904. A piezoelectric resonator array 2900,when acoustically coupled to a material layer (e.g., material layer 102of FIG. 1) can operate with a particular acoustic resonance. When atouch event is occurring, the touch event can cause the piezoelectricresonator array 2900 to resonate differently. This change in acousticresonance due to the touch event can be detected and used as a sensorsignal in an ultrasonic input device, such as instead of a PMUT.Additionally, the piezoelectric cantilevers 2902 can be driven to flexand thus induce emitted signals.

FIG. 30 is a schematic diagram of a piezoelectric resonator array 3000containing piezoelectric pillars 3002 usable in an ultrasound inputdevice according to certain aspects of the present disclosure. Thepiezoelectric resonator array 3000 can contain a set of piezoelectricpillars 3002 on a base 3004. A piezoelectric resonator array 3000, whenacoustically coupled to a material layer (e.g., material layer 102 ofFIG. 1) can operate with a particular acoustic resonance. When a touchevent is occurring, the touch event can cause the piezoelectricresonator array 3000 to resonate differently. This change in acousticresonance due to the touch event can be detected and used as a sensorsignal in an ultrasonic input device, such as instead of a PMUT.Additionally, the piezoelectric pillars 3002 can be driven to flex andthus induce emitted signals. The piezoelectric pillars 3002 can bearranged in any suitable pattern, such as a hexagonal grid.

Aspects of embodiments can be implemented in the form of control logicusing hardware circuitry (e.g. an application specific integratedcircuit or field programmable gate array) and/or using computer softwarewith a generally programmable processor in a modular or integratedmanner. As used herein, a processor can include a single-core processor,multi-core processor on a same integrated chip, or multiple processingunits on a single circuit board or networked, as well as dedicatedhardware. Based on the disclosure and teachings provided herein, aperson of ordinary skill in the art will know and appreciate other waysand/or methods to implement embodiments of the present invention usinghardware and a combination of hardware and software.

Any of the software components or functions described in thisapplication may be implemented as software code to be executed by aprocessor using any suitable computer language such as, for example,Java, C, C++, C#, Objective-C, Swift, or scripting language such as Perlor Python using, for example, conventional or object-orientedtechniques. The software code may be stored as a series of instructionsor commands on a computer readable medium for storage and/ortransmission. A suitable non-transitory computer readable medium caninclude random access memory (RAM), a read only memory (ROM), a magneticmedium such as a hard-drive or a floppy disk, or an optical medium suchas a compact disk (CD) or DVD (digital versatile disk), flash memory,and the like. The computer readable medium may be any combination ofsuch storage or transmission devices.

Such programs may also be encoded and transmitted using carrier signalsadapted for transmission via wired, optical, and/or wireless networksconforming to a variety of protocols, including the Internet. As such, acomputer readable medium may be created using a data signal encoded withsuch programs. Computer readable media encoded with the program code maybe packaged with a compatible device or provided separately from otherdevices (e.g., via Internet download). Any such computer readable mediummay reside on or within a single computer product (e.g. a hard drive, aCD, or an entire computer system), and may be present on or withindifferent computer products within a system or network. A computersystem may include a monitor, printer, or other suitable display forproviding any of the results mentioned herein to a user.

Any of the methods described herein may be totally or partiallyperformed with a computer system including one or more processors, whichcan be configured to perform the steps. Thus, embodiments can bedirected to computer systems configured to perform the steps of any ofthe methods described herein, potentially with different componentsperforming a respective step or a respective group of steps. Althoughpresented as numbered steps, steps of methods herein can be performed ata same time or at different times or in a different order. Additionally,portions of these steps may be used with portions of other steps fromother methods. Also, all or portions of a step may be optional.Additionally, any of the steps of any of the methods can be performedwith modules, units, circuits, or other means of a system for performingthese steps.

The specific details of particular embodiments may be combined in anysuitable manner without departing from the spirit and scope ofembodiments of the invention. However, other embodiments of theinvention may be directed to specific embodiments relating to eachindividual aspect, or specific combinations of these individual aspects.

The above description of example embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdescribed, and many modifications and variations are possible in lightof the teaching above.

A recitation of “a”, “an” or “the” is intended to mean “one or more”unless specifically indicated to the contrary. The use of “or” isintended to mean an “inclusive or,” and not an “exclusive or” unlessspecifically indicated to the contrary. Reference to a “first” componentdoes not necessarily require that a second component be provided.Moreover reference to a “first” or a “second” component does not limitthe referenced component to a particular location unless expresslystated. The term “based on” is intended to mean “based at least in parton.”

All patents, patent applications, publications, and descriptionsmentioned herein are incorporated by reference in their entirety for allpurposes. None is admitted to be prior art.

As used below, any reference to a series of examples is to be understoodas a reference to each of those examples disjunctively (e.g., “Examples1-4” is to be understood as “Examples 1, 2, 3, or 4”).

Example 1 is a method comprising: emitting, by a transducer coupled to afirst surface of a material layer that has a distance between the firstsurface and a second surface, an ultrasonic signal directed toward thesecond surface; detecting, by the transducer, a reflected ultrasonicsignal; determining an amplitude of the reflected ultrasonic signal;determining the amplitude is less than a threshold associated with aportion of the ultrasonic signal penetrating the second surface; andwhen the amplitude is less than the threshold, generating a signalindicating a touch input on the second surface.

Example 2 is the method of example(s) 1, further comprising: detecting,by the transducer, an additional reflected ultrasonic signal, whereinthe additional reflected ultrasonic signal is associated with an echo ofthe reflected ultrasonic signal; determining an additional amplitude ofthe additional reflected ultrasonic signal; and updating the amplitudeby adding the additional amplitude prior to determining the amplitude isless than the threshold.

Example 3 is the method of example(s) 1 or 2, wherein the ultrasonicsignal comprises a first frequency and a second frequency, and themethod further comprises: determining a first amplitude associated withthe first frequency and a second amplitude associated with the secondfrequency; determining the first amplitude and the second amplitude areless than the threshold; and when the first amplitude and the secondamplitude are less than the threshold, generating the signal indicatingan input touch on the second surface.

Example 4 is the method of example(s) 1-3, wherein the material layercomprises at least one or more of glass, metal, leather, wood, ceramic,plastic, and stone.

Example 5 is the method of example(s) 1-4, wherein determining theamplitude of the reflected ultrasonic signal comprises one of:rectifying and integrating the detected ultrasonic signal; accumulatingabsolute values of the detected ultrasonic signal; and squaring andintegrating the detected ultrasonic signal.

Example 6 is the method of example(s) 5, wherein determining theamplitude of the reflected ultrasonic signal further comprises applyingan energy measurement window envelope to the reflected ultrasonicsignal.

Example 7 is the method of example(s) 5 or 6, wherein determining theamplitude of the reflected ultrasonic signal comprises accumulatingabsolute values of the detected ultrasonic signal, and whereinaccumulating absolute values of the detected ultrasonic signal comprisesapplying a negative clocked direct current charge to a switch-capacitoranalog accumulator.

Example 8 is the method of example(s) 1-7, wherein determining theamplitude of the reflected ultrasonic signal is performed by analogcircuitry of an application specific integrated circuit coupled to thetransducer.

Example 9 is the method of example(s) 1-8, further comprising:calculating a moving average of the amplitude of the reflectedultrasonic signal; and calculating the threshold based on the movingaverage.

Example 10 is a method comprising: emitting, by a transducer coupled toa first surface of a material layer that has a distance between thefirst surface and a second surface, an ultrasonic signal directed towardthe second surface; detecting, by the transducer, a reflected ultrasonicsignal; determining an energy value associated with the reflectedultrasonic signal; determining the energy value is less than a thresholdassociated with a portion of the ultrasonic signal penetrating thesecond surface; and when the energy value is less than the threshold,generating a signal indicating a touch input on the second surface.

Example 11 is the method of example(s) 10, further comprising detecting,by the transducer, an additional reflected ultrasonic signal, whereinthe additional reflected ultrasonic signal is associated with an echo ofthe reflected ultrasonic signal, wherein the energy value is furtherassociated with the additional reflected ultrasonic signal.

Example 12 is the method of example(s) 10 or 11, wherein determining theenergy value is performed by analog circuitry of an application specificintegrated circuit coupled to the transducer.

Example 13 is the method of example(s) 10-12, wherein determining theenergy value comprises: rectifying the reflected ultrasonic signal toprovide a rectified signal; integrating a portion of the rectifiedsignal to provide an integrated signal; and measuring, by an analog todigital converter, the integrated signal to determine the energy value.

Example 14 is the method of example(s) 10-12, wherein determining theenergy value comprises: calculating absolute values of the detectedreflected ultrasonic signal; accumulating the absolute values associatedwith the detected reflected ultrasonic signal to provide an accumulatedsignal; and measuring, by an analog to digital converter, theaccumulated signal to determine the energy value.

Example 15 is the method of example(s) 10-12, wherein determining theenergy value comprises: squaring the detected reflected ultrasonicsignal by passing the reflected ultrasonic signal through a self-mixingcircuit to provide a squared signal; integrating the squared signal toprovide an integrated signal; and measuring, by an analog to digitalconverter, the integrated signal to determine the energy value.

Example 16 is the method of example(s) 10-15, further comprising:calculating a moving average of the amplitude of the reflectedultrasonic signal; and calculating the threshold based on the movingaverage.

Example 17 is a device comprising: a body comprising an interior surfaceand an exterior surface; a transducer coupled to the interior surface; acircuit coupled with the transducer and configured to: emit anultrasonic signal directed toward the exterior surface; detect, usingthe transducer, a set of at least one reflected ultrasonic signal;determine an amplitude of the set of at least one reflected ultrasonicsignal; determine the amplitude is less than a threshold, wherein thethreshold is associated with a portion of the at least one ultrasonicsignal penetrating the exterior surface; and when the amplitude is lessthan the threshold, generate a signal indicating a touch input on theexterior surface.

Example 18 is the device of claim 17, wherein the set of at least onereflected ultrasonic signal includes a first reflected ultrasonic signaland a second reflected ultrasonic signal, wherein the second reflectedultrasonic signal is associated with an echo of the first reflectedultrasonic signal.

Example 19 is the device of example(s) 17 or 18, wherein the devicecomprises a mobile phone.

Example 20 is the device of example(s) 17-19, wherein the devicecomprises at least one or more of a steering wheel, an infotainmentinput, a console control a keypad.

Example 21 is the device of example(s) 17-20, wherein the body comprisesat least one or more of glass, metal, leather, wood, and stone.

Example 22 is the device of example(s) 17, 18, or 20-21, wherein thedevice comprises a robot finger input device.

Example 23 is the device of example(s) 17-22, wherein the circuitcomprises one or more processors and a memory coupled to the transducer,wherein the memory includes a plurality of instructions for detectingthe touch input that, when executed by the one or more processors causethe device to perform the steps the circuit is configured to perform.

Example 24 is the device of example(s) 17-23, further comprising anadditional transducer coupled to the interior surface, wherein thecircuit is further coupled to the additional transducer and configuredto: emit an additional ultrasonic signal directed toward the exteriorsurface; detect, using the additional transducer, an additionalreflected ultrasonic signal associated with the additional ultrasonicsignal; determine an additional amplitude of the additional reflectedultrasonic signal; determine the additional amplitude is less than anadditional threshold, wherein the additional threshold is associatedwith a portion of the additional ultrasonic signal penetrating theexterior surface; and generate the signal indicating the touch input onthe exterior surface when the additional amplitude is less than theadditional threshold and when the amplitude is less than the threshold.

Example 25 is the device of example(s) 24, wherein the additionalultrasonic signal has a different frequency than the ultrasonic signal.

Example 26 is the device of example(s) 24 or 25, wherein the transducerand the additional transducer are concentric.

Example 27 is the device of example(s) 24-26, wherein the transducer andthe additional transducer are coupled to a single circuit board.

Example 28 is the device of example(s) 17-27, wherein the transducer isa piezoelectric micromachined ultrasonic transducer.

Example 29 is the device of example(s) 17-28, wherein the transducercomprises a plurality of channels including a set of transmittingchannels and at least one receiving channel, wherein the at least onereceiving channel is positioned between a subset of the set oftransmitting channels.

Example 30 is the device of example(s) 17-29, wherein the circuitcomprises an application specific integrated circuit comprising analogcircuitry, and wherein determining the amplitude is performed using theanalog circuitry of the application specific integrated circuit.

1. A method comprising: emitting, by a transducer coupled to a firstsurface of a material layer that has a distance between the firstsurface and a second surface, an ultrasonic signal directed toward thesecond surface; detecting, by the transducer, at least one reflectedultrasonic signal; determining an amplitude of the at least onereflected ultrasonic signal, wherein determining the amplitude of the atleast one reflected ultrasonic signal comprises inputting a negativedirect current signal and the at least one reflected ultrasonic signalto an accumulation circuit; determining the amplitude is less than athreshold associated with a portion of the ultrasonic signal penetratingthe second surface; and when the amplitude is less than the threshold,generating a signal indicating a touch input on the second surface. 2.The method of claim 1, further comprising: detecting, by the transducer,at least one additional reflected ultrasonic signal, wherein the atleast one additional reflected ultrasonic signal is associated with anecho of the at least one reflected ultrasonic signal; determining anadditional amplitude of the at least one additional reflected ultrasonicsignal; and updating the amplitude by adding the additional amplitudeprior to determining the amplitude is less than the threshold.
 3. Themethod of claim 1, wherein the ultrasonic signal comprises a firstfrequency and a second frequency, and the method further comprises:determining a first amplitude associated with the first frequency and asecond amplitude associated with the second frequency; determining thefirst amplitude and the second amplitude are less than the threshold;and when the first amplitude and the second amplitude are less than thethreshold, generating the signal indicating an input touch on the secondsurface.
 4. The method of claim 1, wherein the material layer comprisesat least one or more of glass, metal, leather, wood, ceramic, plastic,and stone.
 5. The method of claim 1, wherein determining the amplitudeof the at least one reflected ultrasonic signal comprises one of:rectifying and integrating the at least one reflected ultrasonic signal;accumulating absolute values of the at least one reflected ultrasonicsignal; and squaring and integrating the at least one reflectedultrasonic signal.
 6. The method of claim 5, wherein determining theamplitude of the at least one reflected ultrasonic signal furthercomprises applying an energy measurement window envelope to the at leastone reflected ultrasonic signal.
 7. The method of claim 5, whereindetermining the amplitude of the at least one reflected ultrasonicsignal comprises accumulating absolute values of the at least onereflected ultrasonic signal, and wherein accumulating absolute values ofthe at least one reflected ultrasonic signal comprises inputting thenegative direct current signal as a negative clocked direct currentcharge to a switch-capacitor analog accumulator.
 8. The method of claim1, wherein determining the amplitude of the at least one reflectedultrasonic signal is performed by analog circuitry of an applicationspecific integrated circuit coupled to the transducer.
 9. The method ofclaim 1, further comprising: calculating a moving average of theamplitude of the at least one reflected ultrasonic signal; andcalculating the threshold based on the moving average.
 10. A methodcomprising: emitting, by a transducer coupled to a first surface of amaterial layer that has a distance between the first surface and asecond surface, an ultrasonic signal directed toward the second surface;detecting, by the transducer, at least one reflected ultrasonic signal;determining an energy value associated with the at least one reflectedultrasonic signal, wherein determining the energy value of the at leastone reflected ultrasonic signal comprises inputting a negative biascurrent and the at least one reflected ultrasonic signal to anintegration circuit; determining the energy value is less than athreshold associated with a portion of the ultrasonic signal penetratingthe second surface; and when the energy value is less than thethreshold, generating a signal indicating a touch input on the secondsurface.
 11. The method of claim 10, further comprising detecting, bythe transducer, at least one additional reflected ultrasonic signal,wherein the at least one additional reflected ultrasonic signal isassociated with an echo of the at least one reflected ultrasonic signal,wherein the energy value is further associated with the at least oneadditional reflected ultrasonic signal.
 12. The method of claim 10,wherein determining the energy value is performed by analog circuitry ofan application specific integrated circuit coupled to the transducer.13. The method of claim 10, wherein determining the energy valuecomprises: rectifying the at least one reflected ultrasonic signal toprovide a rectified signal; integrating a portion of the rectifiedsignal to provide an integrated signal; and measuring, by an analog todigital converter, the integrated signal to determine the energy value.14. The method of claim 10, wherein determining the energy valuecomprises: calculating absolute values of the at least one reflectedultrasonic signal; accumulating the absolute values associated with theat least one reflected ultrasonic signal to provide an accumulatedsignal; and measuring, by an analog to digital converter, theaccumulated signal to determine the energy value.
 15. The method ofclaim 10, wherein determining the energy value comprises: squaring theat least one reflected ultrasonic signal by passing the at least onereflected ultrasonic signal through a self-mixing circuit to provide asquared signal; integrating the squared signal to provide an integratedsignal; and measuring, by an analog to digital converter, the integratedsignal to determine the energy value.
 16. The method of claim 10,further comprising: calculating a moving average of the energy value ofthe at least one reflected ultrasonic signal; and calculating thethreshold based on the moving average.
 17. A device comprising: a bodycomprising an interior surface and an exterior surface; a transducercoupled to the interior surface; a circuit coupled with the transducerand configured to: emit an ultrasonic signal directed toward theexterior surface; detect, using the transducer, a set of at least onereflected ultrasonic signal; determine an amplitude of the set of atleast one reflected ultrasonic signal, wherein determining the amplitudeof the set of at least one reflected ultrasonic signal comprisesinputting a negative direct current signal and the set of at least onereflected ultrasonic signal to an accumulation circuit; determine theamplitude is less than a threshold, wherein the threshold is associatedwith a portion of the ultrasonic signal penetrating the exteriorsurface; and when the amplitude is less than the threshold, generate asignal indicating a touch input on the exterior surface.
 18. The deviceof claim 17, wherein the set of at least one reflected ultrasonic signalincludes a first reflected ultrasonic signal and a second reflectedultrasonic signal, wherein the second reflected ultrasonic signal isassociated with an echo of the first reflected ultrasonic signal. 19.The device of claim 17, wherein the device comprises a mobile phone. 20.The device of claim 17, wherein the device comprises at least one ormore of a steering wheel, an infotainment input, a console control akeypad.
 21. The device of claim 17, wherein the body comprises at leastone or more of glass, metal, leather, wood, and stone.
 22. The device ofclaim 17, wherein the device comprises a robot finger input device. 23.The device of claim 17, wherein the circuit comprises one or moreprocessors and a memory coupled to the transducer, wherein the memoryincludes a plurality of instructions for detecting the touch input that,when executed by the one or more processors cause the device to performthe steps the circuit is configured to perform.
 24. The device of claim17, further comprising an additional transducer coupled to the interiorsurface, wherein the circuit is further coupled to the additionaltransducer and configured to: emit an additional ultrasonic signaldirected toward the exterior surface; detect, using the additionaltransducer, an additional reflected ultrasonic signal associated withthe additional ultrasonic signal; determine an additional amplitude ofthe additional reflected ultrasonic signal; determine the additionalamplitude is less than an additional threshold, wherein the additionalthreshold is associated with a portion of the additional ultrasonicsignal penetrating the exterior surface; and generate the signalindicating the touch input on the exterior surface when the additionalamplitude is less than the additional threshold and when the amplitudeis less than the threshold.
 25. The device of claim 24, wherein theadditional ultrasonic signal has a different frequency than theultrasonic signal.
 26. The device of claim 24, wherein the transducerand the additional transducer are concentric.
 27. The device of claim24, wherein the transducer and the additional transducer are coupled toa single circuit board.
 28. The device of claim 17, wherein thetransducer is a piezoelectric micromachined ultrasonic transducer. 29.The device of claim 17, wherein the transducer comprises a plurality ofchannels including a set of transmitting channels and at least onereceiving channel, wherein the at least one receiving channel ispositioned between a subset of the set of transmitting channels.
 30. Thedevice of claim 17, wherein the circuit comprises an applicationspecific integrated circuit comprising analog circuitry, and whereindetermining the amplitude is performed using the analog circuitry of theapplication specific integrated circuit.